This invention relates generally to aircraft ejection seats, and more particularly to means for positioning and restraining the limbs of a crewmember in an ejection seat during ejection.
High performance military and other aircraft are frequently equipped with systems to effect escape of crewmembers when a stricken aircraft is about to crash. The most common such escape system is the open ejection seat, which, upon initiation propels itself and its occupant through the aircraft canopy and away from the aircraft.
Upon ejection from an aircraft, however, a crewmember in an open ejection seat may be subjected to an extremely high wind blast. This wind blast, often on the order of several hundred knots, can cause the crewmember's limbs to flail, resulting in severe injuries. In order to reduce flail injuries, various devices have been proposed which utilize combinations of straps, nets, or bladders to restrain the arms and legs of a crewmember in an aircraft ejection seat during ejection. One highly effective leg restraint system currently fielded by the United States military comprises a cable or lanyard which is attached to the airframe by means of a shear fastener. The other end of the lanyard is attached to the crewmember's ankles by means of leg garters which must be “hooked in” as the crewmember prepares for flight. The lanyard passes through a one-way jam-cleat or “snubber.” When the ejection seat is activated, as the ejection seat moves up and out of the aircraft, movement of the ejection seat causes the lanyard to be pulled through the snubber. This draws the leg garters in against the seat thereby restraining the crewmember's legs. At a predetermined threshold, the shear fastener breaks thereby arresting any further inward motion of the crewmember's legs. The snubber then retains the lanyard in position as the ejection seat exits the aircraft.
Although highly effective, the prior art leg restraint system is considered an “active” system in that it requires to the crewmember to “hook in” in order for it to be readied for flight. Accordingly, the prior art leg restraint may be improperly attached or ignored by the crewmember rendering it ineffective. Various “passive” limb retention systems have been proposed to remedy this problem. U.S. Pat. No. 4,247,064 to Schulman et al. discloses an ejection seat including a pair of rigid hooks that are actuated by gas generators to capture and restrain the crewmember's legs during ejection. U.S. Pat. No. 4,359,200 to Brevard et al. discloses an ejection seat with a plurality of inflatable bladders that inflate to capture and restrain the crewmember's limbs. U.S. Pat. No. 4,667,902 to Zenobi discloses an ejection seat equipped with a pair of nets that deploy to capture and restrain the crewmember's arms during ejection. Each of the foregoing inventions adds substantial complexity and weight to the ejection seat. Consequently, the “active” leg restraint system has remained the standard in spite of its acknowledged drawbacks. Accordingly, what is needed is a “passive” limb retention system that is as lightweight, simple and reliable as the current “active” system, but without the drawback of requiring the crewmember to “hook in” for it to be readied for flight.